Spontaneous thymic hemorrhage in a normal thymus in neonates and infants has been reported in the literature. Only one case of spontaneous thymic hemorrhage in an adult has been reported to our knowledge. We herein report the case of an adult who had a cardiac operation 26 years previously and who was on anticoagulation. He experienced acute hemorrhage in a normal thymus, and this was not thought to be attributable to an accidental cause such as trauma or to hypertension.